Boron cluster compounds are a kind of distinctive covalent species with a unique molecular architecture, nonconventional cluster bonding, and unusual chemistry. They show rather specific properties not encountered in other types of compounds [1]. As this field of chemistry has been developed rapidly for almost half a century, major advances in theory and experiment on the boranes and carboranes have been established, and they have shown many practical applications [2, 3]. Siloxane-linked polymers containing m-carborane icosahedral units show extraordinary chemical and thermal stability. Derivatives of carboranes have been used in the areas of boron neutron capture therapy (BNCT) for tumors [4]. Besides, carboranes and their derivatives have also been used to synthesize catalysts [5], radiopharmaceuticals [6], polymers [7], and coordination compounds [8]. Among the known polyhedral carboranes, 1,2-dicarba-c/oso-dodecaborane (o-carborane) has been intensively studied due to its relatively easy preparation [9].

As the CH groups of o-carborane are weakly acidic and can be deprotonated by strong base such as «-bu-tyllithium [10], it can be used to prepare a kind of mononuclear 16e half-sandwich complexes of Co, Rh, Ir, Ru, and Os containing a chelating 1,2-dicarba-closo-dodecaborane-1,2-dichalcogenolate ligand [8—13]. These sterically congested, coordinatively unsaturated compounds can be stored conveniently and used for

the completion of various chemical transformations [11]. As the metal atoms of these half-sandwich complexes are coordinatively and electronically unsaturat-ed, they can combine metal fragments to afford novel homometallic or heterometallic clusters containing metal-metal bonds [12]. They react with Lewis bases to give their corresponding 18-electron stable species [13]. Furthermore, the metal centers of these 16e compounds are electronically deficient and metal-chalcogen bonds are reactive, which render them interesting candidates for reactions with alkynes [14].

In the course of preparing the above mononuclear 16e compounds, some other binuclear [15—18], trinu-clear [19], and multinuclear [20] carborane products have been successfully isolated. Furthermore, some species have shown further reactivity toward organic molecules [18, 21]. Recently, we have isolated a binuclear MeCp-cobalt carborane complex (II) in the course of preparing the mononuclear MeCp-cobalt carborane complex MeCpCoS2C2B10H10 (I). To the best of our knowledge, the studies on the two carborane complexes are relatively less explored. Herein, we report the syntheses of the above carborane compounds I, II, their further reactivity toward organic molecules and preparation of complexes III and IV. Synthesis of complexes I—IV is given in Scheme.

H

.Co

s'

\

LiS

SLi i

C

C

m (i)

C^Co s S

PhC=CH

Or"

Co-S

(iii)

MeO ___

C

MeO2CCsCCO2Me

O

O

MeO

Co.

C MeO2CCsCCO2Me or PhCsCH "

\

C

(IV)

(II)

Scheme.

EXPERIMENTAL

Materials and methods. All experiments were carried out under an argon atmosphere using standard Schlenk techniques. Solvents were dried by refluxing over sodium (petroleum ether, ether, and THF) or calcium hydride (dichloromethane) under nitrogen and then distilled prior to use. «-Butyllithium (2.0 M in cyclohexane, Aldrich), o-carborane (Acros), phe-nylacetylene (Alfa Aesar), dimethyl acetylene dicar-boxylate (Aldrich) and other chemicals were used as commercial products without further purification. MeCpCoS2C2B10H10 (I) was prepared according to literature [22]. Elemental analysis was performed in an elementar vario EL III elemental analyzer. NMR data were recorded on a Bruker DRX-500 spectrometer. 1H NMR and 13C NMR spectra were reported in ppm with respect to CHCl3/CDCl3 (8 1H = 7.26, 8 13C = 77.0) and 11B NMR spectra were reported in ppm with respect to external Et2O-BF3 (8 11B = 0). The IR spectra were recorded on a Bruker Vector 22 spectrophotometer with KBr pellets in the 4000—400 cm-1 region. The mass spectra were recorded on Micromass GC-TOF for EI-MS (70 eV).

Synthesis of complexes I and II. To a solution of o-carborane (57.7 mg, 0.4 mmol) in dry diethylether (20 mL) was added a 2.0 M solution of «-butyllithium (0.4 mL, 0.8 mmol). After 30 min, sulfur (26.3 mg, 0.82 mmol) was added, followed by addition of MeCpCo(CO)I2 (163.7 mg, 0.39 mmol) in dry THF (25 mL) at 0°C. The resulting mixture was stirred for 0.5 h, and then the temperature gradually rose to ambient temperature. The solvents were evaporated under reduced pressure. The components of the residue

Synthesis of complex III. To a solution of I (103 mg, 0.3 mmol) in dry CH2Cl2 (20 mL) was added phenylacetylene (107 mg, 1.2 mmol). The resulting mixture was stirred for 10 h at ambient temperature. After removal of the solvent, the residue was chro-matographed on silica gel. Elution with petroleum ether-CH2Cl2 (1 : 2 v/v) gave pure compound III (64 mg, 48%) as black solid. Suitable single crystal of III was obtained by slow diffusion of petroleum ether into its CH2Cl2 solution.

X-ray crystallography. Suitable single crystals of II, III, and IV were selected and mounted in air onto thin glass fibers. X-ray diffraction data were collected on a Bruker SMART APEX II CCD diffractometer at 291(2) K using Mo^ radiation (X = 0.71073 A) by multi-scan mode. The SAINT program was used for integration of the diffraction profiles. The structures were solved by direct methods using the SHELXS-97 [23] program package and refined against F2 by full-matrix least-squares with SHELXL-97 [24]. All non-hydrogen atoms were refined with anisotropic thermal

parameters. Hydrogen atoms on carbon were set in calculated positions and refined as riding. The crystal-lographic data are summarized in Table 1 and selected bond lengths and angles are listed in Table 2 containing the supplementary crystallographic data for this article. Copies of the data can be obtained free of charge from the Cambridge Crystallographic Data Centre (nos. 1045892 (II), 1045